The present invention relates to a skewed axis inertial sensor assembly for supporting a plurality of gyros and accelerometers. More specifically, the present invention relates to an inertial sensor assembly for providing a redundant strap down system including six gyroscopes and six accelerometers arranged with their input axis in a particular relationship.
Use of redundant strap down inertial reference units in both commercial aviation and space applications is well known in the art. Redundancy concepts are intended to achieve significant improvement in reliability, and thus enhance mission success. Generally, a redundant strap down inertial navigation system utilizes two or three discrete inertial reference units. Each inertial reference unit generally includes a discrete inertial sensor apparatus for producing sensor data, and associated electronics for signal processing and generation of inertial reference data. Inertial sensor apparatuses generally include three discrete gyros and three discrete accelerometers for the production of necessary data required for producing inertial reference and/navigational information. All three gyros and all three accelerometers and their respective electronics must be operative in an inertial reference unit, as described, to produce complete inertial reference data.
Many navigational systems of prior art aircraft utilize three redundant inertial reference units, similar to that just described, and therefore would include a total of nine gyros and nine accelerometers. In such systems, it should be understood that any one sensor of the combination of three gyros and three accelerometers in the inertial reference unit results in the failure of the inertial reference unit--i.e., the output data therefrom is no longer valid.
Another inertial reference system having redundant inertial reference unit capability was proposed and described in a paper entitled, "A Redundant Strap Down Inertial Reference Unit (SIRU)", by Gerald P. Gilmore, et al, Journal of Spacecraft and Rockets, Vol. 9, No. 1, January 1972, pages 39-47. The Gilmore system is comprised of six gyros having their input axis skewed relative to each other in accordance with a specific relationship, and six accelerometers having their input axis skewed relative to each other in accordance with a specific relationship. This six gyro/six accelerometer redundant inertial reference system provides a fail operative to two failures and fail safe to the third failure operative system.
In the Gilmore, et al, publication, six gyros and six accelerometers are arranged with each input axis thereof in alignment with a symmetrical pattern that corresponds to the normal to faces of a dodecahedron. Each of the gyros and accelerometers are separately packaged with its calibrated electronics in a module and mounted to a ".pi.-frame". This configuration enables data processing with self contained failure isolation for up to two out of six of either sensor type, and continued operation with as many as three out of six failures of the same failure type.
The Gilmore, et al, system provides what is sometimes referred to as a fault tolerant inertial navigation system which is highly reliable. The failure detection and isolation of such a system is described in a paper entitled, "Fault Tolerant Highly Reliable Inertial Navigational System", by Mahesh Jeerage, et al, IEEE PLANS, 1956, pp 456-460.